There is a need for high performance cylinder heads which can be simply retrofitted onto existing short blocks for off-highway, high horsepower automotive application. There is also a need for a limited, mass production, high performance cylinder heads for "limited editions" of certain automobiles having high performance capabilities which can generate a suitable torque curve over the load speed range. In addition, there is a need for mass produced high performance, gasoline fueled, internal combustion engines for power generators and commerical truck applications which can compete with diesel engines.
In considering the design of any high performance cylinder head, one that achieves high horsepower coordinated and matched with increased torque, there are a number of basic, engine-valve train as well as head considerations that might be initially considered. For example, it is known that an in-line valve arrangement in the head driven by conventional push rods from a single cam shaft within the short block provides certain inherent features ideally suited for high performance engines of the type this invention relates to which is not present, for example, in an overhead, camshaft arrangement. The basic shape of the combustion chamber must be considered (wedge shaped or hemispherical) and it is known that conventional, wedge shaped chambers allow for a flat burn control surface, known as a "quench" surface and it is known to modify the shape of the quench surface to achieve certain distribution of gas flows within the head. Another consideration rests in the shape of the piston head and it is known that flat head pistons are particularly desirable for use with wedge shaped combustion chambers for the applications to which the present invention is particularly suited. The volumetric size and accordingly, the compression ratio, must be established. It is a common practice to achieve an increase in the combustion ratio of the engine by deck milling the mounting surface of the head to reduce the size of the combustion chamber. The actual valve sizes must be established within the confines of the space available in the combustion chamber and then matched to the desired horsepower and the torque.
Once the general design of the head is established by considering factors such as those discussed above, the specific objective becomes one of determining how to contour the combustion chamber and form the runners or intake and exhaust passages in the head to permit adequate ingress and egress of the gases so that the internal combustion engine can adequately "breathe" at high speed. More specifically, when the valve area in the combustion chamber is significantly increased to improve horsepower, eddy flow currents are established, the effects of which hinder the intake of the gases into and the exhaust of the gases out of the combustion chamber. In addition, since the valves must be placed closely adjacent one another a shrouding effect occurs therebetween causing an uneven flow of the gases about the valves.
One approach, discussed in the cited article and now almost uniformly followed to improve "breathing" is the use of multiple valves in each combustion chamber. While the benefits of a multi-valve application for general purpose automotive use is not questioned, the application of multiple valves for the high performance internal combustion engines to which this invention relates is not practical. Such an arrangement requires overhead camshafts and the associated timing chain which does not afford the precise opening and closing of the valves at high speed inherently present in the push rod arrangement while also providing a further drain of engine power. More importantly though, is the simple fact that for a given combustion chamber size, two valves can occupy a greater space than three or four valves.
A more sensible approach to provide improved breathing in a two-valve arrangement is set forth in our parent patent. In our prior patent we contoured the chamber, modified the quench surface, and added a mass buildup to a portion of the chamber to achieve a funnelled, increased velocity, gas flow to and from the seats. This dramatically improved the breathing and consequently the horsepower and torque of the internal combustion engine at high speeds (i.e. in excess of 5,000 rpm). Such problems have been significantly eliminated, in good part, by contouring the combustion chamber to, in effect by funneling the gases to and from the valve seats by an especially configured contour which extended from the seats to the quench surface. In our parent patent and in keeping with the philosophy of increased velocity and mass flow through the valve seats, the exhaust and intake runners or passageways in the head were likewise modified to permit ingress and egress of the gases with as little back pressure as possible. More specifically, the intake valve passageway was modified to provide a flow restriction in the runner or passageway to increase the velocity of the air flow through the intake passageway while maintaining a high mass flow. It was found in certain high speed instances (well in excess of 5,000 rpm) that the gasoline in the fuel-air mixture admitted into the intake passageway from the fuel injectors did not completely atomize or "splashed" resulting in an uneven burning of the mixture within the chamber. It was also discovered that because of the close spacing between the valves (and despite the funnel contoured shape of the chamber including the mass buildup) at very high speed operation, at which time the exhaust valve is not completely seated while the intake valve is opening (i.e. valve overlap), a portion of the fuel-air mixture exiting the intake runner through the intake valve was sucked or short circuited out the exhaust valve. This results in a smaller volume of fuel-air mixture within the combustion chamber for combustion purposes than that which would otherwise be available while also exhausting the unburnt mixture as an emission pollutant.
A problem unrelated to the high speed performance of our improved head inherent in all modified, high performance engines is the inability of the internal combustion engine to produce acceptable torque at lower speeds or rpms. This presents a limitation in the use of the cylinder head of our prior invention in commercial vehicles and to some extent, in the high performance, limited edition vehicles occasionally produced by the automobile manufacturers. Again, the approach followed in the art was to increase engine torque by increasing the air flow into the combustion chamber at lower speeds.